Nearly 3,000 civilians have disappeared in Syria since the uprising against President Assad's regime began in March, an activist group has said.

Their families and friends say they have no idea where they are, but the government has denied any knowledge of the whereabout of these people. Human rights group Avaaz says it believes they are most likely to have been covertly detained, or killed.

Will Davies of Avaaz told the Huffington Post that people who have "re-appeared" say they have been tortured in prison. He also suspects that many of the missing people are in fact dead because protestors who have been shot during demonstrations often have their bodies snatched away by the security forces.

Avaaz has calculated that the government crackdown on its citizens has meant that one person every hour has disappeared since March.

At least 1,600 demonstrators have been killed and there are an additional 12,617 people also in detention, but they have been publicly declared to have been detained. Avaaz's campaign, which launched on Thursday, highlights the plight of the 2,918 people who have simply disappeared.

President Assad's regime has made information difficult to obtain, but Avaaz has worked with three Syrian human rights groups to compile a list of missing people.

They have verified the list by collecting the names and photos of each missing person and have undertaken the lengthy process of speaking to each missing person's family or close friends.

Unlike the tens of thousands arrested, these people are classified as "disappeared" because the regime has refused to admit taking them. One such incident took place in Damascus on the 2 July. Ahmad Ziadeh, 55, was taken when regime intelligence officers raided his workplace. His daughter, Lila, 25, says her family do not know why.

"The intelligence agents were following him on his way to work. He noticed them and called me from his office. They came in and talked to him, but he was still seeing a client so had a few minutes before they took him," she told Avaaz.

"He asked one of them their name and when he went back to finish his meeting with his client he left a note on his desk with their details. We went to find him, but they denied that they had taken him. I have had to go into hiding, as the intelligence agents have been asking my friends about me. I don't stay in one place for more than two days."

Stories like this are commonplace across the country.

Muntaha (who does not use her real name for her own safety) is a widow who has visited every security branch in her city looking for her son, Yazan. He is 16 and joined a protest march nearly two months ago. Friends say he was taken away after security forces battered him until he lost consciousness. "Yazan did not vanish," Muntaha told the group.

"The security forces have him".

Security forces have apparently warned Muntaha to stop looking for her son and threaten to take her older son, if she continues to ask about Yazan.

The regime's sweeps have been intensifying over the past week, in the lead-up to the Holy Month of Ramadan, which begins next week.